How to create a tree-like list on a site for filtering?

Question

WordPress

There is a list of different clinics. And they have such a filtering according to the list of Services with a tree structure ( www.1nep.ru/clinics/)

and I need to do the same according to the example, only my own. So that I can add my services to any clinic. Now I do all this through custom fields. But I can't figure out how to make this tree-like list and filter records by it.

Answer 1

select2